Abstract:

Refrigerating device formed by a main compressor (190), a condenser (140)
downstream of and in fluid communication with the main compressor (190),
main expansion means (170) downstream of the condenser (140) and an
evaporator (180) downstream of and in fluid communication with the main
expansion means (170), which also comprises a turbocompressor unit (160)
in fluid communication between the evaporator (180) and the main
compressor (190) and a heat exchanger (150, 152) having a hot branch
(150c) connected upstream, via an inlet line (145), to the condenser
(140) and downstream, via an outlet line (149), to the main expansion
means (170) and a cold branch (15Of) connected, upstream, to an expansion
means (142, 144) mounted on a branch (146) of the line (145) and,
downstream, to a turbine portion (162) of the turbocompressor unit (160).
The invention also relates to a method for circulating a refrigerating
fluid inside the abovementioned device.

Claims:

1. Refrigerating device comprising a main compressor, a condenser
downstream of and in fluid communication with said main compressor, main
expansion means downstream of said condenser and an evaporator downstream
of and in fluid communication with said main expansion means,said
refrigerating device characterized in that it comprises a turbocompressor
unit in fluid communication between said evaporator and said main
compressor and at least one heat exchanger having a hot branch connected
upstream, via an inlet line, to said condenser and downstream, via an
outlet line, to said main expansion means and a cold branch connected,
upstream, to an expansion means mounted on a branch of said line and,
downstream, to a turbine portion of said turbocompressor unit.

2. Device according to claim 1, characterized in that said at least one
heat exchanger is a tube-bundle heat exchanger.

3. Device according to claim 1, characterized in that said at least one
heat exchanger is a plate-type heat exchanger.

4. Device according to claim 1, characterized in that said expansion means
is an isoenthalpic throttling valve.

5. Device according to claim 1, characterized in that it comprises a first
and a second heat exchanger arranged in series between said heat
exchanger and said main expansion means and in that said turbocompressor
unit comprises a first and a second turbine portion, said second heat
exchanger having a hot branch in fluid communication, via a connection
line, with the hot branch of said first heat exchanger and a cold branch
connected, upstream, to an expansion means mounted on a branch of said
line and, downstream, to said second turbine portion of said
turbocompressor unit (160).

6. Method for circulating a refrigerating fluid comprising:compressing the
refrigerating fluid in a main compressor;condensing the fluid in a
condenser downstream of and in fluid communication with said main
compressor;expanding the fluid in main expansion means downstream of said
condenser;evaporating the fluid in an evaporator downstream of and in
fluid communication with said main expansion means;said method
characterized in that it comprises:between said condensation stage and
said expansion stage at least one stage involving heat exchange, inside
at least one heat exchanger, between the compressed refrigerating fluid
circulating inside a hot branch of the heat exchanger and an associated
amount of the compressed refrigerating fluid bled-off upstream of the
heat exchanger, cooled inside an expansion means and flowing inside a
cold branch of the heat exchanger; andbetween said main expansion stage
and said main compression stage, a stage involving pre-compression of the
refrigerating fluid inside a turbocompressor unit, said pre-compression
stage comprising at least one stage involving expansion, inside at least
one turbine portion of the turbocompressor unit, of the bled-off amount
of refrigerating fluid, leaving the cold branch of the heat exchanger.

7. Method according to claim 6, characterized in that it comprises,
downstream of said at least one heat exchange stage between said
condensation stage and said expansion stage:a second stage involving heat
exchange in a second heat exchanger arranged in series with the at least
one exchanger between the refrigerating fluid leaving the hot branch of
the at least one heat exchanger and circulating inside the hot branch of
the second exchanger and an associated amount of the refrigerating fluid
bled-off upstream of the heat exchanger, cooled inside an expansion means
(144) and circulating in the cold branch;and in that said pre-compression
stage between said main expansion stage and main compression stage is
powered by expansion, in a first and second turbine portion of said
turbocompressor unit, of the bleed-offs from each heat exchanger.

8. Device according to claim 2, characterized in that it comprises a first
and a second heat exchanger arranged in series between said heat
exchanger and said main expansion means and in that said turbocompressor
unit comprises a first and a second turbine portion, said second heat
exchanger having a hot branch in fluid communication, via a connection
line, with the hot branch of said first heat exchanger and a cold branch
connected, upstream, to an expansion means mounted on a branch of said
line and, downstream, to said second turbine portion of said
turbocompressor unit.

9. Device according to claim 3, characterized in that it comprises a first
and a second heat exchanger arranged in series between said heat
exchanger and said main expansion means and in that said turbocompressor
unit comprises a first and a second turbine portion, said second heat
exchanger having a hot branch in fluid communication, via a connection
line, with the hot branch of said first heat exchanger and a cold branch
connected, upstream, to an expansion means mounted on a branch of said
line and, downstream, to said second turbine portion of said
turbocompressor unit.

10. Device according to claim 4, characterized in that it comprises a
first and a second heat exchanger arranged in series between said heat
exchanger and said main expansion means and in that said turbocompressor
unit comprises a first and a second turbine portion, said second heat
exchanger having a hot branch in fluid communication, via a connection
line, with the hot branch of said first heat exchanger and a cold branch
connected, upstream, to an expansion means mounted on a branch of said
line and, downstream, to said second turbine portion of said
turbocompressor unit.

Description:

TECHNICAL FIELD OF THE INVENTION

[0001]The present invention relates to a refrigerating device, in
particular suitable for circulating a fluid in industrial refrigerating
plants as well as in household air-conditioning systems, and to a method
for circulating a refrigerating fluid associated with it.

DESCRIPTION OF THE PRIOR ART

[0002]In general, a device for circulating a refrigerating fluid includes
a compressor designed to compress the refrigerant in the gaseous state,
giving it a higher temperature and pressure value; a condenser able to
condense the compressed gaseous refrigerant with consequent conversion
thereof into the liquid state and release of heat to the external
environment; an expansion unit, for example a capillary tube or an
isoenthalpic throttling valve, intended to lower the temperature and the
pressure of the refrigerant; and an evaporator, which absorbs heat from
the external environment, cooling it, and transfers it to the
refrigerating fluid at a low temperature and pressure received from the
expansion unit, said fluid passing from the liquid state into the vapour
state.

[0003]During recent years many attempts have been made to increase the
performance of the refrigerating devices. Some have encountered obstacles
of a technological nature, which have prejudiced the feasibility thereof,
while others have brought advantages in terms of increased efficiency,
while significantly complicating, however, the plant. An example in this
connection consists of dual-stage compression plants where the existence
of two independent compressors causes problems of balancing of the loads
and more complex management of the entire plant.

[0004]The object of the present invention is to eliminate, or at least
reduce, the drawbacks mentioned above, by providing a refrigerating
device and a method for circulating refrigerating fluid associated with
it, which are improved in terms of efficiency.

[0005]According to a first aspect of the present invention, a
refrigerating device comprising a main compressor, a condenser downstream
of and in fluid communication with said main compressor, main expansion
means downstream of said condenser and an evaporator downstream of and in
fluid communication with said main expansion means is provided,

[0006]characterized in that it comprises a turbocompressor unit connected
between said evaporator and said main compressor and at least one heat
exchanger having a hot branch connected upstream, via an inlet line, to
said condenser and downstream, via an outlet line, to said main expansion
means and a cold branch connected, upstream, to an expansion means
mounted on a branch of said inlet line and, downstream, to a turbine
portion of said turbocompressor unit.

[0007]According to another aspect of the present invention a method for
circulating a refrigerating fluid inside a device according to the
invention is provided, said method comprising the stages of:
[0008]compressing the refrigerating fluid in a main compressor;
[0009]condensing the fluid in a condenser downstream of and in fluid
communication with said main compressor; [0010]expanding the fluid in
main expansion means downstream of said condenser; [0011]evaporating the
fluid in an evaporator downstream of and in fluid communication with said
main expansion means;

[0012]characterized in that it comprises [0013]between said condensation
stage and said expansion stage at least one stage involving heat exchange
stage, inside at least one heat exchanger, between the compressed
refrigerating fluid, which flows inside a hot branch of the heat
exchanger, and an associated amount of compressed refrigerating fluid
withdrawn upstream of the heat exchanger, cooled inside an expansion
means and flowing inside a cold branch of the heat exchanger; and
[0014]between said main expansion stage and said main compression stage,
a stage involving pre-compression of the refrigerating fluid inside a
turbocompressor unit, said pre-compression stage comprising at least one
stage involving expansion, inside at least one turbine portion of the
turbocompressor unit, of the bled-off refrigerating fluid leaving the
cold branch of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]Characteristic features and advantages of the present invention will
emerge more clearly from the following detailed description of a
currently preferred example of embodiment thereof, provided solely by way
of a non-limiting example, with reference to the accompanying drawings,
in which:

[0016]FIG. 1 is a schematic view, which shows a refrigerating device
according to the prior art;

[0020]In the accompanying drawings, identical or similar parts and
components are indicated by the same reference numbers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIGS. 1 and 2 show, respectively, a refrigerating device 10 of the
conventional type, which is particularly suitable for freezing alimentary
products, and the p-h (pressure-enthalpy) diagram for the fluid
circulating inside it. As shown, the device 10 is formed by a compressor
12, by a condenser 14 in fluid communication with the compressor 12, by
an isoenthalpic throttling valve 16 in fluid communication with the
condenser 14 and by an evaporator in fluid communication with the
throttling valve 16, upstream, and with the compressor 12 downstream.

[0022]The refrigerating fluid, for example freon, enters into the
compressor 12 in the form of superheated vapour at a low temperature and
pressure, for example -35° C. and 1.33 bar (point 1* in p-h
diagram), is compressed and enters into the condenser 14 at a high
pressure and temperature, for example +65° C. and 16 bar (point 2*
in p-h diagram). Inside the condenser 14 the refrigerating fluid
undergoes cooling, passing from the superheated vapour state (point 2*)
into the liquid state (point 3* in p-h diagram) and releasing a quantity
of heat qout to the external environment. The refrigerating fluid in
the liquid state, leaving the condenser 14, expands passing through the
isoenthalpic throttling valve 16 and undergoing a reduction in pressure
without exchanging heat with the external environment (isoenthalpic
conversion). The fluid leaving the throttling member (point 4* in p-h
diagram) enters into the evaporator, where it passes from the liquid
state into the superheated vapour state (point 1* in p-h diagram)
absorbing a quantity of heat qin from the external environment.

[0023]With reference to FIG. 3, which shows a preferred embodiment of the
present invention, a device for circulating a refrigerating fluid,
denoted generally by the reference number 100, is formed by the
components of a conventional refrigerating device, namely a main
condenser 140, main expansion means such as a main isoenthalpic
throttling valve 170, an evaporator 180 and a main compressor 190.

[0024]The aforementioned conventional device is supplemented with certain
components, enclosed ideally within a block--defined by broken lines in
FIG. 3--which comprises a first and a second heat exchanger, 150, 152,
respectively, for example heat exchangers of the plate or tube-bundle
type, commonly used in the refrigerating sector, arranged in series
between the condenser 140 and the main throttling valve 170, and a
turbocompressor unit 160, inserted between the main compressor 190 and
the evaporator 180 and provided with a compressor portion 166 and a first
and second turbine portion 162, 164, which are respectively supplied by
an outlet of each heat exchanger 150, 152.

[0025]More particularly the condenser 140 is connected, via an inlet line
145, to a circuit for refrigerating fluid at a higher temperature,
referred to below as "hot branch" 150c, of the first heat exchanger 150.
The inlet line 145 has, branched off it, a line 146 which incorporates
first expansion means, for example a first throttling valve 142, which
leads into a circuit for a refrigerating fluid at a lower temperature,
referred to below as "cold branch" 150f, of the first heat exchanger 150.
The outlet of the hot branch 150c of the first heat exchanger 150 is
linked, via a connection line 147, to the inlet of a circuit for
refrigerating fluid at a higher temperature, referred to below as "hot
branch" 152c, of the second heat exchanger 152, while the outlet of the
cold branch 150f of the first heat exchanger 150 is connected to the
inlet of the first turbine portion 162 of the turbocompressor unit 160.

[0026]The line 147 connecting together the first and the second heat
exchanger 150, 152 has a branch 148 provided with second expansion means,
for example a second throttling valve 144, which leads into a circuit for
refrigerating fluid at a lower temperature, referred to below as "cold
branch" 152f, of the second heat exchanger 152. The outlet of the hot
branch 152c of the second heat exchanger is connected, via an outlet line
149, to the main throttling valve 170, while the outlet of the cold
branch 152f is connected to the inlet of the second turbine portion 164
of the turbocompressor unit 160.

[0027]The outlet of the evaporator 180 is connected to the inlet of the
compressor portion 166 of the turbocompressor unit 160, the outlet of
which is in fluid communication with the main compressor 190.

[0028]Below the operating principle of the device according to FIG. 3 will
be described with reference to the p-h diagram relating to the
refrigerating fluid circulating through it, shown in FIG. 4. In the
particular example in question, the refrigerating device is used for
rapid freezing of alimentary products. For this purpose, the temperatures
of the fluid circulating inside the device vary between a value
Tmin=-40° C. and a value Tmax=63.7° C. and the
refrigerating fluid chosen is freon. It is understood that the
refrigerating device according to the present invention is suitable for
many applications, for example the air-conditioning of domestic premises,
so that, depending on the intended use, the pressure and temperature
values of the physical states 1-14, as well as the type of refrigerating
fluid circulating inside the device, will vary correspondingly.

[0029]Refrigerating fluid, typically freon, at a temperature
T5=35° C. and pressure p5=16.1 bar (point 5 in p-h
diagram), namely in a liquid/vapour equilibrium state, flows out from the
condenser 140. A portion of the refrigerating fluid flowing out from the
condenser 140, referred to below as first bleed-off s1, is conveyed, via
the branch 146 of the line 145 into the first isoenthalpic throttling
valve 142, where it is cooled down to a temperature ranging between the
maximum temperature (Tmax=35° C.) and the minimum temperature
(Tmin=-35° C.) of the cycle, preferably a temperature
T9=7° C. (point 9 in p-h diagram; p9=7.48 bar) and then
into the cold branch 150f of the first heat exchanger 150, while the
remaining portion 1-s1 of refrigerating fluid enters directly into the
cold branch 150c of the heat exchanger 150 at the temperature T5 and
at the pressure p5.

[0030]Inside the first heat exchanger 150, the refrigerating fluid portion
contained in the hot branch 150c transfers heat to the refrigerating
fluid portion contained in the cold branch 150f, being cooled from
T5=35° C. to a temperature T6=12° C., and
entering the subcooled liquid zone of the p-h diagram (point 6;
p6=16.1 bar), while the refrigerating fluid portion contained in the
cold branch 150f absorbs heat from the refrigerating fluid portion
contained in the hot branch 150c, being heated from T9=7° C.
to a temperature T10=12° C. and entering the superheated
vapour zone of the p-h diagram (point 10; p10=7.48 bar).

[0031]Downstream of the first heat exchanger 150 a second amount of
refrigerating fluid is bled off, so that a portion s2 of the subcooled
liquid leaving the hot branch 150c passes through the second isoenthalpic
throttling valve 144, where it is further cooled from the temperature
T6=12° C. to a temperature T12=-17° C. (point 12
in p-h diagram; p12=3.38 bar) and then into the cold branch 152f of
the second heat exchanger 152, while the remaining portion 1-s1-s2 of the
refrigerating fluid leaving the heat exchanger 150 enters into the hot
branch 152c of the second heat exchanger 152 at the temperature T6
and pressure p6.

[0032]Inside the second heat exchanger 152, the portion of refrigerating
fluid contained in the hot branch 152c releases heat to the refrigerating
fluid portion contained in the cold branch 152f, cooling from
T6=12° C. to a temperature T7=-12° C. and moving
further to the left, in the diagram of FIG. 4, into the subcooled liquid
zone (point 7 in p-h diagram; p7=16.1 bar), while the refrigerating
fluid portion contained in the cold branch 152f absorbs heat from the
refrigerating fluid portion contained in the hot branch 152c, being
heated from T12=-17° C. to a temperature T13=-12°
C. and entering the superheated vapour zone of the p-h diagram (point 13;
p13=3.38 bar).

[0033]The first and second bleed-offs of refrigerating fluid s1, s2
leaving each heat exchanger 150, 152 in the form of refrigerating fluid
in the superheated vapour state are introduced, respectively, into the
first and second turbine portion 162, 164 of the turbocompressor unit
160. Inside the first turbine portion 162, the refrigerating fluid
undergoes expansion, passing from a pressure p10=7.48 bar
(T10=12° C.) to a pressure p11=2.03 bar
(T11=-25° C.); similarly, inside the second turbine portion
164 the refrigerating fluid will undergo expansion passing from a
pressure p13=3.38 bar (T13=-12° C.) to a pressure
p14=2.3 bar (T14=-25.6° C.).

[0034]The portion of refrigerating fluid 1-s1-s2 leaving the hot branch
152c of the second heat exchanger 152 (point 7 in p-h diagram) enters
into the main throttling valve 170, cooling from T7=-12° C.
to a temperature T8=-40° C. (point 8 in p-h diagram;
p8=1.33 bar) and then into the evaporator 180, where it passes from
the liquid+vapour state to the superheated vapour state (point 1 in p-h
diagram), absorbing a quantity of heat Qin from the external
environment. The refrigerating fluid in the superheated vapour state
leaving the evaporator 180 enters into the compressor portion 166 of the
turbocompressor unit 160.

[0035]The compressor 166, operated by the turbines 162, 164 hosting,
inside them, the conversion, into mechanical energy, of the kinetic
energy contained in the bled-off refrigerating fluid s1 and s2 in the
superheated vapour state supplied by the first and second heat exchanger
150, 152, performs pre-compression of the refrigerating fluid supplied by
the evaporator 180 (point 3 in p-h diagram; T3=-22.1° C., p3=2.03
bar), before its entry into the main compressor 190.

[0036]This pre-compression stage offers considerable advantages. Firstly,
since the mechanical energy is supplied by the bleed-offs s1, s2 which
expand inside the turbines 162, 164, it is not required to use an
external energy source. Secondly, the turbocompressor unit 160 compresses
the refrigerating fluid, performing the work LTC (FIG. 4), when it
is in the maximum specific volume condition, so that the main compressor
190 does not perform that part of the work which, in view of its
constructional characteristics, penalizes its efficiency and in
particular its processable mass flow, with a consequent reduction in the
electric energy supplying the compressor itself. Again, the
turbocompressor unit 160 has a fluid/dynamic connection with the main
compressor 190 with the possibility of being able to adapt independently
to the different load conditions without the aid of external control.
Finally, it is important to mention the fact that cooling of the
refrigerating fluid produced in the heat exchangers 150, 152 causes an
increase in the performance of the evaporator 180, despite the fact that,
following the bleed-offs s1, s2 there is, at the same time, a
simultaneous reduction in the flow of refrigerating fluid into the
evaporator 180.

[0037]The refrigerating fluid pre-compressed in turbocompressor unit 160
enters into the main compressor 190, where it is compressed to a pressure
p4=16.1 bar (point 4 in p-h diagram; T4=63.7), and then
conveyed to the inlet of the condenser 140.

[0038]It has been found that, with a device for circulating refrigerating
fluid according to the present invention, namely comprising a
pre-compression stage performed by a turbocompressor unit, it is possible
to achieve a coefficient of performance (COP), defined as the ratio
between the heat Q drawn from the lower temperature source, which
constitutes the "amount of cold" produced and the work L expended in
order to cause operation of the device for circulating a refrigerating
fluid, which is greater than that of a conventional device of the type
illustrated in FIGS. 1 and 2.

[0039]In particular, assuming the pressures of the bleed-offs s1 and s2 to
be, respectively, of p9=7.48 bar and p12=3.38 bar, a minimum
temperature gradient ΔTmin=5° C. in the heat exchangers
150, 152, an efficiency πT=0.85 of the first and second turbine
portion 162, 164, an efficiency πC=0.80 of the compressor portion
166 and an efficiency πCP=0.75 of the main compressor 190, the
pressure values ({circumflex over (p)}), temperature values (T) and
enthalpy values (h) are obtained for the physical states 1-14 of the p-h
diagram according to FIG. 4, shown in the following Table 1:

[0040]The coefficient of performance COP is defined, in general, as the
ratio between the heat Q subtracted from the lower temperature source,
which constitutes the "amount of cold" produced, and the work L expended
to cause operation of the refrigerating fluid circulation device. In
particular, the COP is defined by the ratio between the heat Qin
subtracted from the external environment by the evaporator 180 and the
work LCP performed by the main compressor 190, namely:

and Qin=(1-s1-s2)×(h1-h7)

LCP=h4-h2

[0041]From which, based on the values shown in Table 1, the following is
obtained:

COP = Q in L CP = 1 , 74 ##EQU00001##

[0042]Table 2 below summarises the typical pressure, temperature and
enthalpy values of a refrigerating fluid circulating inside a
conventional refrigeration device of the type illustrated in FIGS. 1 and
2.

[0044]from which, based on the values shown in Table 2, the following is
obtained:

COP ST = q in L CP = 1 , 34 ##EQU00002##

[0045]The percentage benefit Δ of the novel refrigerating device
compared to a refrigerating device of the conventional type is:

From the

[0046] Δ = COP - COP ST COP ST ≈ 30 %
##EQU00003##

description provided hitherto it is possible to state that a refrigerating
device according to the present invention, owing to the presence of the
turbocompressor unit 160 and the consequent pre-compression of the
refrigerating fluid circulating inside the device upstream of the main
compressor 190, allows an increase in performance equal to about 30% to
be obtained, all of which without the need for power supplied externally,
but advantageously using the mechanical energy provided by one or more
turbine portions 162, 164 of the turbocompressor unit 160, obtained by
causing the expansion of one or more amounts s1, s2 of refrigerating
fluid bled-off downstream of the condenser 140.

[0047]Although the invention has been described with reference to a
preferred example thereof, persons skilled in the art will understand
that it is possible to apply numerous modifications and variations
thereto, all of which fall within the scope of protection defined by the
accompanying claims. For example, instead of two heat exchangers and
turbocompressor unit with two turbines, it is possible to use a single
heat exchanger and a turbocompressor unit with a single turbine. In this
specific case, the single heat exchanger will have the hot branch
connected between the condenser and the main throttling valve and the
cold branch in fluid communication with the inlet of the single turbine
portion of the turbocompressor. Moreover, instead of a turbocompressor
unit having multiple turbine portions, it is possible to envisage a
plurality of turbocompressors each with a single turbine portion.